(a) Field of the Invention
Broadly speaking this invention relates to personnel access control systems. More particularly, in a preferred embodiment, this invention relates to personnel access control systems to the type that employ optically-encoded identification cards and the like.
(b) Discussion of the Prior Art
The recent dramatic increases in industrial espionage, terrorism and employee dishonestly have caused many industrial and governmental organizations to carefully re-examine the security procedures by which employees, business invitees and guests are admitted to restricted premises. These studies have demonstrated that the most commonly used personnel access control technique, the conventional photo-I.D. card, is not very effective due to the relative ease by which such I.D. cards can be forged or altered, especially by experienced criminals or trained terrorists.
As a result of the limitations of conventional photo-I.D. cards, many organizations have experimented with the use of more sophisticated access control systems which typically rely on personnel descriptors such as the employee's voiceprint, finger-prints, signature, et cetera. Unfortunately, such systems are very expensive, exceedingly complex and most difficult to maintain in working condition. Further, despite their complexity, these systems do not offer the degree of security that was originally hoped for because experience has shown that the human voice can be imitated; that fingerprints can be surreptitiously "lifted" and recreated in latex; and that signatures can be forged. There is, thus, great interest in a return to the time-proven and far less expensive photo-I.D. card access control system, provided, of course, that greater immunity to card alteration can somehow be provided.
It has been suggested that the incorporation of a hidden code word or symbol within the I.D. card would make it much more difficult to forge or alter the card. Such a system would have the further advantage that if the forger were unaware that the I.D. card bore a hidden code word and merely altered the employee photograph and identification data on the card, the hidden code word could be used to detect the alteration, resulting in the immediate apprehension of the would-be intruder.
Unfortunately, heretofore the only practical way to implant a hidden code word in an I.D. card was to use some suitable magnetic recording medium, capacitance medium, or optical transmission medium. For example, a magnetic stripe buried beneath the surface of the card was commonly employed. The difficulty with this approach is that it is very easy to detect the presence of such a magnetized region and almost as easy to alter the code word stored therein. Additionally, a lost, encoded card can be used by the unauthorized card finder causing a breach in security. As a result, the return to a simpler access control system has been frustrated for want of a truly secure I.D. card.